<style>
    * { margin:0; padding:0; font:12px Verdana; }
    .overflow { float:left; width:90px; height:40px; border:5px solid #555; color:#555; }
    .sibling { border:5px solid #999; color:#999; width:100px; }
</style>

<div style="width:100px; height:20px; border:5px solid black">
    <div class="overflow">OVERFLOW OVERFLOW</div>
</div>
<div class="sibling">SIBLING SIBLING</div>
<br />
<div style="width:100px; height:60px; border:5px solid black">
    <div class="overflow" style="margin-top:30px;">OVERFLOW OVERFLOW</div>
</div>
<div class="sibling">SIBLING SIBLING</div>